How to define the primary key for an Eloquent model in Laravel?

In Laravel's Eloquent model, you can define the primary key by setting the $primaryKey property in the model class. By default, Laravel assumes that the primary key is an auto-incrementing integer, but you can customize it based on your requirements.

Here's an example of how to define the primary key for an Eloquent model in Laravel:

namespace App\Models;

use Illuminate\Database\Eloquent\Model;

class YourModel extends Model
{
    /**
     * The primary key associated with the table.
     *
     * @var string
     */
    protected $primaryKey = 'your_primary_key_column';

    // Rest of your model code...
}

Replace 'your_primary_key_column' with the actual name of the column you want to use as the primary key in your database table.

If you want to use a non-incrementing or non-numeric primary key, you should also set the $incrementing property to false and define the $keyType property with the appropriate data type. Here's an example:

namespace App\Models;

use Illuminate\Database\Eloquent\Model;

class YourModel extends Model
{
    /**
     * Indicates if the primary key is auto-incrementing.
     *
     * @var bool
     */
    public $incrementing = false;

    /**
     * The data type of the primary key.
     *
     * @var string
     */
    protected $keyType = 'string';

    /**
     * The primary key associated with the table.
     *
     * @var string
     */
    protected $primaryKey = 'your_primary_key_column';

    // Rest of your model code...
}

In the above example, $incrementing is set to false to indicate that the primary key is not auto-incrementing, and $keyType is set to 'string' to define the data type of the primary key.